4:00 PM - 4:15 PM
[AAS11-15] Characteristics of dynamical and chemical fields in Chemistry Climate Models
Keywords:Chemistry Climate Model, stratospheric dynamics and chemistry, extratropical upper troposphere and lower stratosphere, tropical tropopause layer
We carefully analyzed differences found at mid-high latitudes in the stratosphere of the winter hemisphere, the extratropical upper troposphere and lower stratosphere (Ex-UTLS) and the tropical tropopause layer (TTL). Comparisons of stratospheric temperatures at mid-high latitudes show that for all FR-CCM results the seasonal change is delayed in both hemispheres during the winter and spring; especially in the southern hemisphere all FR-CCM results show cold biases in early spring. Results for ozone are similar to those for temperature, and the biases in the southern hemisphere are clearer than in the northern hemisphere. We also investigated the Eliassen-Palm fluxes (EP flux) and resulting residual mean meridional circulations, because the seasonal changes in temperature and ozone during these seasons and in those regions are affected by the meridional circulation. EP flux convergences and downward velocities in winter are smaller for all FR-CCM results than SD-CCM ones, indicating that the time of maximum wave activities seen in EP fluxes are delayed about 1-2 months for all FR-CCM results. These suggest that the temperature and ozone biases are due to some problems with model reproducibility of planetary waves propagating into the stratosphere from the troposphere.
In the Ex-UTLS, all FR-CCM results show cold biases especially in summer, and all SD-CCM results overestimate radiative cooling effects. Comparisons of water vapor with satellite observations (Aura-MLS) and models show that all model results overestimate water vapor in the upper troposphere at mid- and high latitudes. Because water vapor has an important role in the radiation budget during the summer in this region, the FR-CCM cold biases and the SD-CCM overestimations of radiative effects are from water vapor overestimations. The dynamical fields are specified in SD-CCM, therefore these overestimations are due to the model reproducibility of chemical, transport and microphysics processes associated with water.
In the TTL, we compared ozone distributions in SD-CCM and FR-CCM results. We found that FR-CCM of MIROC3.2-CCM and WACCM4 cannot reproduce the increase of ozone in boreal summer. This is due to the annual cycle of upwelling and the horizontal transport from mid latitude; this mechanism is called in-mixing and is understood as the nearly isentropic transport owing to the Asian and North American monsoon anticyclones. WACCM4 FR-CCM can reproduce this increase in isentropic coordinate, and the Asian monsoon anticyclone is weak in the FR-CCM of MIROC3.2-CCM. These indicate that temperature and monsoon anticyclone reproducibility is strongly related to the improvement of ozone results in the TTL.